1. Field of the Invention
The present invention relates to a method of manufacturing a minute structure, and to a minute structure and a minute structure device manufactured by the manufacturing method. More particularly, the present invention relates to a method of manufacturing an ordered minute structure by forming a recess-projection pattern in the surface of a substrate or on the substrate by means of interference lithography, irradiation with a focused ion beam, or the like. The present invention also relates to a minute device characterized by using an orderly minute structure as a mold or a mask.
2. Related Background Art
Some thin films, wires, dots, or the like of metals and semiconductors, having a size smaller than a specific length, confine motions of electrons to exhibit a unique electrical, optical or chemical characteristic. From this point of view, there is a growing interest in minute structures of nano-sizes having a structure smaller than several hundred nanometers (also called nanostructures) as a high-performance material.
Methods for manufacturing such nanostructures include a method of directly manufacturing a nanostructure by a semiconductor processing technique, e.g., photolithography, electron beam lithography, x-ray lithography, etc. Methods of forming a very fine pattern are reported by, for example, M. C. Hutley, xe2x80x9cCoherent Photofabricationxe2x80x9d, Optical Engineering, Vol. 15 No. 3(1976), and J. Y. Decker et al, xe2x80x9cGeneration of subquarter-micron resist structures using optical interference lithography and image reversalxe2x80x9d, J. Vac. Sci. Technol, B15(6), November/December(1997).
Besides the development of these manufacturing methods, trials have been made to realize novel nanostructures on the basis of orderly structures spontaneously formed, i.e., structures formed in a self-ordering manner.
As a method of such self-ordering, an anodizing method can be mentioned which enables easy controllable manufacture of a structure having nano-sized pores (nanoholes). For example, anodic alumina produced by anodizing Al or an Al alloy in an acid bath is known.
If an Al plate is anodized in an acid electrolyte, a porous oxide membrane is formed (see, for example, R. C. Furneaux, xe2x80x9cThe formation of controlled-porosity membranes from anodically oxidized aluminiumxe2x80x9d, NATURE, Vol. 337, P147(1989), etc.). Specifically, this porous oxide membrane has a unique geometric structure in which very thin cylindrical pores (nanoholes) having a diameter of several nanometers to several hundred nanometers are arrayed at intervals of several nanometers to several hundred nanometers (cell size).
A method of performing two anodizing steps in order to improve the verticality, linearity and independence of such pores has been proposed. In this method, a porous oxide membrane formed by anodizing is temporarily removed and is again processed by anodizing to make a porous oxide membrane having pores (Masuda et al, xe2x80x9cFabrication of gold nanodot array using anodic porous alumina as an evaporation maskxe2x80x9d, Jpn. J. Appl. Phys, Vol. 35, Part 2, No. 1B, L126-L129(1996)).
Further, a method of forming pore formation start points by using a stamper in order to improve the controllability of the shape, interval and pattern of pores of a porous oxide membrane has been proposed (Japanese Patent Application Laid-Open No. 10-121292, EP-A-931859). That is, in this method, dents are formed as pore formation start points in the surface of an Al plate by pressing a substrate having a plurality of projections against the surface of the Al plate, and anodizing is thereafter performed to make a porous oxide membrane having pores. Japanese Patent Application Laid-Open No. 11-200090, and EP-A-0913850 publication, etc. Also disclose contents relating to porous oxide membranes having pores.
Various applications of anodic alumina have been tried by considering the unique geometrical structure of anodic alumina. For example, applications to membranes utilizing the wear resistance and electric insulation of anodic oxide film, and to filters in the form of a separated membrane are known. By using a technique of filling nanoholes with a metal, a semiconductor or the like, or a nanohole replication technique, applications to coloring, magnetic recording mediums, electroluminescent elements, electrochromic elements, optical elements, solar cells, gas sensors, and other various applications are now being tried. Further, applications to quantum effect devices, such as quantum wires, and metal-insulator-metal devices, to molecule sensors using nanoholes as a chemical reaction field, and other various applications are expected (Masuda, xe2x80x9cHighly-Ordered Nanohole-Array from Anodic Porous Aluminaxe2x80x9d, Kotaibutsuri (solid state physics), Vol. 31, No. 5, 493-499(1996)).
There is a demand for a simple method for manufacturing nano-sized structures with improved reproducibility.
However, there is a limit in terms of controllability, to the improvement of methods based on ordinary anodizing and/or there is a limit to the interval between formable pores, and the material needs to be anodized for a long time.
In view of the above-described problems of the conventional art, an object of the present invention is to provide, in a method of manufacturing a structure having pores (nanostructure) made by anodizing, techniques for making, in a simple manner, any desired array of pores having a large area in a short time at a low cost.
Another object of the present invention is to provide a novel structure and device formed on the basis of a structure having nano-sized pores made by using these techniques to enable versatile uses of structures having nano-sized holes as functional materials.
To achieve the above-described objects, according to the present invention, there is provided a method of manufacturing a structure having pores, including the steps of preparing a substrate having recesses in its surface, providing a film to be anodized on a surface of the substrate, and anodizing the film.
According to the present invention, the substrate may have a first layer, a conductive layer provided on the first layer, and a second layer provided on the conductive layer, the second layer having in its portion a through hole through which the conductive layer is exposed.
According to the present invention, the substrate may have a first layer, a conductive layer provided on the first layer, and a second layer provided on the conductive layer. The second layer may be provided in such a manner that the conductive layer is partially exposed.
According to the present invention, the step of preparing the substrate includes the step of providing the second layer. The step of providing the second layer may include the steps of providing on the conductive layer a material to form the second layer, performing at least two steps of interference lithography to process the material provided to form the second layer, and partially exposing the conductive layer by removing a region exposed by the interference lithography. The direction of interference fringes in each of the second and other subsequent interference lithography steps is different from the direction of interference fringes in the first step of interference lithography.
According to the present invention, the step of providing the second layer may alternatively include the steps of providing on the conductive layer a material to form the second layer, performing at least two steps of interference lithography to process the material provided to form the second layer, and partially exposing the conductive layer by removing a region other than a region exposed by the interference lithography. The direction of interference fringes in each of the second and other subsequent interference lithography steps is different from the direction of interference fringes in the first step of interference lithography.
According to the present invention, the substrate having recesses in its surface may include a first layer, and a second layer provided on the surface of the first layer, the second layer having in its portion a through hole through which the first layer is exposed.
According to the present invention, the substrate having recesses in its surface may include a first layer, and a second layer provided on the first layer. The second layer may be provided in such a manner that the first layer is partially exposed.
According to the present invention, the electric conductivity of the second layer is lower than the electric conductivity of the conductive layer.
The above-described manufacturing method makes it possible to form orderly pores through a large area.
According to the manufacturing method of the present invention, recesses (pore formation start points) in the surface of the film to be anodized are formed right above recesses of a xe2x80x9crecess-projection patternxe2x80x9d provided on the substrate. Therefore, when pores (nanoholes) are formed by anodizing, the pores can be formed with improved linearity.